[pfranz]

I really wish I could have thought of some specifics to make my point better. Most professional photographers do know basics of exposure really well, but may not know things like the inverse-square law when applying to flash photography (especially with the newer flash systems out there). Instead of using a light meter to take careful measurements, they fall back on abstractions, trial and error, and rules of thumb--like sunny 16 rule, their experience, and looking at the back of the LCD.

The only example I can think of is that I've heard Paul McCartney can't read or write sheet music.

Some people (like myself), feel the need to understand the underlying technologies in order to become competent. I don't feel like that's the only way to competency.